Hetero-integration of functional semiconductor layers and devices has received strong research interest from both academia and industry. While conventional techniques such as pick-and-place and wafer ...bonding can partially address this challenge, a variety of new layer transfer and chip-scale transfer technologies have been developed. In this review, we summarize such transfer techniques for heterogeneous integration of ultrathin semiconductor layers or chips to a receiving substrate for many applications, such as microdisplays and flexible electronics. We showed that a wide range of materials, devices, and systems with expanded functionalities and improved performance can be demonstrated by using these technologies. Finally, we give a detailed analysis of the advantages and disadvantages of these techniques, and discuss the future research directions of layer transfer and chip transfer techniques.
Modular multilevel converters (MMCs) have been widely used in recent years due to their superior advantages in medium/high-voltage applications. The finite control set model predictive control ...(FCS-MPC) has shown high dynamic responses for the control of the MMC. However, with the existing FCS-MPC algorithms, the steady-state performances are degraded due to the irregular pulse patterns, especially under unbalanced grid conditions. In this paper, based on the discrete state-space model of the MMC, a modulated MPC (M2PC) algorithm is proposed to overcome the aforementioned drawback of the FCS-MPC. Compared to FCS-MPC algorithms, the M2PC accurately calculates and tracks the reference circulating current and adopts an effective modulation method, and, in turn, the proposed M2PC can obtain enhanced steady-state ac-side/circulating currents control performances under unbalanced grid conditions, with the high dynamic-state performances of the conventional FCS-MPC algorithms reserved. Experimental results regarding one typical FCS-MPC algorithm and the proposed M2PC algorithm are comparatively evaluated in detail for the steady/dynamic-state performances and pulse patterns by a downscaled prototype. The effectiveness and feasibility of the proposed M2PC are clearly validated by the experimental results.
TiAl alloys are lightweight, show decent corrosion resistance and have good mechanical properties at elevated temperatures, making them appealing for high-temperature applications. However, ...polysynthetic twinned TiAl single crystals fabricated by crystal-seeding methods face substantial challenges, and their service temperatures cannot be raised further. Here we report that Ti-45Al-8Nb single crystals with controlled lamellar orientations can be fabricated by directional solidification without the use of complex seeding methods. Samples with 0° lamellar orientation exhibit an average room temperature tensile ductility of 6.9% and a yield strength of 708 MPa, with a failure strength of 978 MPa due to the formation of extensive nanotwins during plastic deformation. At 900 °C yield strength remains high at 637 MPa, with 8.1% ductility and superior creep resistance. Thus, this TiAl single-crystal alloy could provide expanded opportunities for higher-temperature applications, such as in aeronautics and aerospace.
In recent years, modular multilevel converters (MMCs) are very popular in medium/high-voltage motor drive systems and high-voltage direct-current (HVDC) applications. The conventional model ...predictive control (MPC) strategies for the MMC are not practical due to their substantial calculation requirements, especially under high number of voltage levels. To solve this problem, a fast MPC strategy combined with a submodule (SM)-voltage sorting balancing method is proposed based on the discrete mathematical model derived for the MMC in this paper. By optimizing the implementation of the control objectives and simplifying the rolling optimization, the proposed strategy is simpler to expand to a system with larger number of SMs, with the amount of calculation reduced and the advantages of the conventional MPC algorithm reserved. In addition, the proposed control can minimize the dv/dt of the output voltages. Both steady-state and transient performances are evaluated by a down-scaled three-phase MMC prototype under various experimental conditions, which validates the proposed fast MPC strategy.
Lactobacillus species dominate the microbiome in the lower genital tract of most reproductive-age women. Producing lactic acid and H2O2, lactobacilli are believed to play an important role in ...prevention of colonization by and growth of pathogens. However, to date, there have been no reported studies characterizing how lactobacilli interact with Chlamydia trachomatis, a leading sexually transmitted bacterium. In this report, we demonstrate inactivation of C. trachomatis infectivity by culture media conditioned by Lactobacillus crispatus, L. gasseri and L. jensenii, known to be dominating organisms in the human vaginal microbiome. Lactobacillus still cultures produced lactic acid, leading to time- and concentration-dependent killing of C. trachomatis. Neutralization of the acidic media completely reversed chlamydia killing. Addition of lactic acid into Lactobacillus-unconditioned growth medium recapitulated the chlamydiacidal activity of conditioned media. The H2O2 concentrations in the still cultures were found to be comparable to those reported for the cervicovaginal fluid, but insufficient to inactivate chlamydiae. Aeration of Lactobacillus cultures by shaking markedly induced H2O2 production, but strongly inhibited Lactobacillus growth and lactic acid production, and thus severely affected acidification, leading to significantly reduced chlamydiacidal efficiency. These observations indicate lactobacilli inactivate chlamydiae primarily through maintaining acidity in a relatively hypoxic environment in the vaginal lumen with limited H2O2, which is consistent with the notion that women with higher vaginal pH are more prone to sexually transmitted C. trachomatis infection. In addition to lactic acid, formic acid and acetic acid also exhibited potent chlamydiacidal activities. Taken together, our findings imply that lowering the vaginal pH through engineering of the vaginal microbiome and other means will make women less susceptible to C. trachomatis infection.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Meander migration results from the interaction between inner bank accretion and outer bank erosion/collapse. This interaction has been usually treated as a long‐term average of a sequence of erosion ...events determined by flow hydrographs. Little attention has been paid to the role that individual bank collapse events play on meander evolution. To fill this gap, we developed a numerical model of river meandering that describes explicitly bank collapse. Results show that as bend curvature increases due to meander migration and elongation, the initially scattered locations of bank collapse events converge toward the channel section where bed shear stress attains a maximum. Simulations illustrate the observed catch‐up behavior between inner and outer banks, driven by intermittent bank collapse events. Moreover, bank collapse is found to speed up short‐term meander migration and, consistent with field observations, meanders turn out to evolve toward a state characterized by constant channel width.
Plain Language Summary
Meanders are one of the most ubiquitous morphological features observed in natural rivers. They consist of a series of alternating bends that, seen from above, display one of the most striking morphological patterns in nature. The migration of meandering rivers is attributed to outer bank retreat, due to erosion, and inner bank accretion, due to deposition. In this work, we propose a morphodynamic model to investigate the effects that repeated bank collapse events have on meander evolution. Our results show that the migration of meander bends can be described through a catch‐up behavior, driven by outer bank collapse and subsequent inner bank accretion, that on average ensures a nearly constant channel width.
Key Points
Meander bend migration is described through a catch‐up behavior, driven by intermittent bank collapse events
As the river bend evolves increasing its apex curvature, bank collapse tends to occur at the location of maximum shear stress
Individual bank collapse events speed up the short‐term migration rate of meandering rivers
Understanding the effect of percolation behavior of complex geometrical pores on the tortuosity and thermal conductivity of porous composites is very crucial to the design and optimization of porous ...composites. In this work, we adopt the continuum percolation theory to accurately determine the nonlinear thermal conductivity and tortuosity of porous composites composed of homogeneous solid matrix and three-dimensional pores of geometrical morphologies from the isotropic sphere to anisotropic polyhedra. Through extensive Monte Carlo simulations and the finite-size scaling analysis, the percolation threshold of spherical and polyhedral pores is obtained. Two continuum percolation-based models are respectively presented to derive the tortuosity and thermal conductivity of porous composites over the whole porosities range, including near the percolation threshold. Comparison with extensive experimental, numerical and theoretical results confirms that the present models are capable of accurately determining the percolation threshold and tortuosity of complex geometrical porous networks and the effective thermal conductivity of porous composites as conductor-superconductor and insulator-conductor media. Furthermore, we use the proposed models to probe the influences of pore shape and porosity on the tortuosity and thermal conductivity of porous composites. The results elucidate the intrinsic interplay of component, structure, and thermal conductivity of porous composites, which can provide sound guidance for porous composite design and evaluation.
Abstract
In this paper, the traditional DSW conditions was presented. The nonlinear incomplete differential conditions were converted into common differential conditions through travelling wave ...transformation, and all the definite voyaging wave arrangements for the traditional DSW conditions can characterized by use a complete separation framework for polynomials. The specific voyaging wave arrangements existed as periodic solutions of geometrical functions and sane numbers, lone wave arrangements, doubly occasional arrangements of elliptic functions.
A novel strategy for the synthesis of cis‐decalins by an ytterbium‐catalyzed asymmetric inverse‐electron‐demand Diels–Alder reaction of 2‐pyrones and silyl cyclohexadienol ethers is reported here. A ...broad range of synthetically important cis‐decalin derivatives with multiple contiguous stereogenic centers and functionalities are obtained in good yields and stereoselectivities. A full set of diastereomeric substituted cis‐decalin motifs are readily accessible by tuning the absolute configurations of substituted silyl cyclohexadienol ethers (R or S) as well as the ligands (R or S). The synthetic potential is showcased by the enantioselective total synthesis of 4‐amorphen‐11‐ol, and further demonstrated by the first total synthesis of cis‐crotonin.
A new strategy for the synthesis of cis‐decalin derivatives is realized by an asymmetric inverse‐electron‐demand Diels–Alder reaction between two different conjugate dienes. With this method, the enantioselective total synthesis of 4‐amorphen‐11‐ol and the first total synthesis of cis‐crotonin have been achieved.
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